How do you keep swimsuits/bras from opening at the top?

So I’m a petite, small chested girl (34A) and I just bought a swimsuit from Victorias Secret that I absolutely LOVE!! However, if I’m not standing with my shoulders back it will open up at the top and you can see straight into my swimsuit! This happens with every single bra as well. Does anyone else have this problem or am I just not buying the right size? If I went down to a 32A does that change the cup size at all?

Is it a halter? are your collapsed shoulders pushing the halter forward or something? Anyway you can find a pic of someone else/post a modest one of yourself? I don’t really understand what is happening.

Edit- a fuller coverage suit will probably have less of this problem, or one with molded cups since the cups will want to stay curved even if your shoulders aren’t in the ideal position. Is it a bandeau? Triangle?

@Equine_Breeder: Do you have breasts that are fuller at the bottom(I think they’re pretty commonly referred to a ‘teardrop’ shaped)? Mine are like that, so ALL my bras have that bizarre gap at the chest, even though they fit/are a little tight.

@kgirl91: It’s a bikini but it looks like a bra pretty much. The cups are curved already. It just gaps at the top. Even my 32A bras do this and it drives me nuts! My FI yells at me al lthe time because my nipples are out but I can’t help it!

@Equine_Breeder: Some ladies need a less structured top due to the shap of their …ahem assets no matter whether they are big or small. I have the same issue with bras and bathing suits that have too much structure to them. As a result I buy bras and bikini tops with less structure so they lay naturally.

Something like this gapes open for me:

While something like this lays flat:

Have you tried a bandeau top for bikinis? They look nice and shouldn’t gape.

As for bras, I prefer Fredericks over VS because their Hollywood Cleavage bra cups my form better than the molded cups at VS.

@Equine_Breeder: The last time I tried on a suit like the one you posted my entire boob and nipple was on display. I love the way they look on the hangar but as soon as I put molded cups on, my nipples immediately escape the confines of the cups.